This application claims the benefit of Korean Patent Application No. 2001-09027, filed on Feb. 22, 2001 in Korea, which is hereby incorporated by reference for all purposes as if fully set forth herein.
1. Field of the Invention
The present invention relates to a liquid crystal display (LCD) device and more particularly, to a transflective liquid crystal (CLC) display device and a method of manufacturing the same.
2. Discussion of the Related Art
Flat panel display devices, which have properties of being thin, and having low weight and low power consumption, have been required as the information age rapidly evolves. The flat panel display device may be classified into two types depending on whether it emits light or not. One is a light-emitting type display device that emits light to display images and the other is a light-receiving display device that uses an external light source to display images. Plasma display panels (PDPs), filed emission display (FED) devices and electro luminescence (EL) display devices are examples of the light-emitting type display devices and liquid crystal displays are an example of the light-receiving type display device. The liquid crystal display device is widely used for notebook computers and desktop monitors, etc. because of its superior resolution, color image display and quality of displayed images.
Generally, the liquid crystal display device has first and second substrates, which are spaced apart and facing each other. Each of the substrates includes an electrode and the electrodes of each substrate are positioned to face each other. A Liquid crystal is interposed between the first substrate and the second substrate. Voltage is applied to the liquid crystal through the electrodes of each substrate, and thus an alignment of the liquid crystal molecules is changed according the applied voltage to display images. Because the liquid crystal display device cannot emit light as described before, it needs an additional light source to display images.
The liquid crystal display device can be classified into two types depending on the type of the light source that is used. One is a transmissive liquid crystal display device and the other is a reflective liquid crystal display device. The transmissive liquid crystal display device displays a color image by irradiating artificial light from a back light, which is positioned behind a liquid crystal panel, to the liquid crystal and then controlling the amount of the light according to the alignment of the liquid crystal. The reflective liquid crystal display device displays a color image by controlling a transmittance of the light according to an alignment of the liquid crystal by reflecting ambient light or artificial light. Because the transmissive liquid crystal display device uses an artificial light source such as the back light, it can display a bright image in dark surroundings but it has a high power consumption. The reflective liquid crystal display device depends on ambient light or an external artificial light source for its light source and accordingly it has lower power consumption than the transmissive liquid crystal display device but it is not suitable for dark surroundings. Accordingly, the transflective liquid crystal display device, which has characteristics of both the transmissive liquid crystal display device and the reflective liquid crystal display device, has been suggested in the field.
FIG. 1 is a cross-sectional view of a conventional transflective liquid crystal display device. As shown in the figure, a pixel electrode 20 is formed on a first substrate 10, referred to as an array substrate, that has a thin film transistor (not shown), i.e., a switching element. The pixel electrode 20 consists of a transmission electrode 21 and a reflection electrode 22. A hole is formed in the reflection electrode 22 and the transmission electrode 21 is formed in the hole. The transmission electrode 21 is formed of transparent conductive material such as indium tin oxide (ITO) or indium zinc oxide (IZO) that has a relatively high transmittance of light. Whereas, the reflection electrode 22 is formed of material such as aluminum (Al) that has a low electric resistance and a high reflectance.
A second substrate 30, i.e., referred to as a color filter substrate, is positioned over the first substrate 10 maintaining a certain distance from the first substrate 10. A color filter 40, which corresponds to the pixel electrode 20, is formed beneath the second substrate 30. The color filter 40 includes sub-color-filters red (R), green (G), and blue (B) and each of the sub-color filters corresponds to each of the pixel electrode 20. A common electrode 50 is formed beneath the color filter 40 using transparent conductive material. A black matrix (not shown) is positioned between the second substrate 30 and the color filter 40 to protect any leakage of light in an area other than the pixel. A liquid crystal layer 60 is positioned between the common electrode 50 and the pixel electrode 20.
A first retardation film 71 and a second retardation film 72 are formed on the outer side of the first substrate 10 and the second substrate 30 respectively. The first retardation film 71 and the second retardation film 72 serve to change the polarization state of light. Because the first and second retardation films 71 and 72 have a phase difference of xcex/4, the first and second retardation films 71 and 72 change linear polarization into circular polarization and circular polarization into linear polarization. A lower polarizer 81 and an upper polarizer 82 are positioned on outer side of the first retardation film 71 and the second retardation film 72, respectively. The light transmission axis of the upper polarizer 82 is perpendicular to the light transmission axis of the lower polarizer 81. A back light 90 is positioned under the lower polarizer 81 and serves as a light source for a transmission mode. The transfective liquid crystal display device is designed on the basis of a reflection mode and thus when a voltage is not applied, the transmittance of the transmission mode is only one-half of the transmittance of the reflection mode. Accordingly, a transflective liquid crystal display device in which the transmittance of the transmission mode is controlled the same as the transmittance of the reflection mode by forming the thickness of a liquid crystal layer of the transmission mode thicker than the thickness of a liquid crystal layer of the reflection mode, has been suggested in the field. The transflective liquid crystal display device is manufactured through a series of process steps like the conventional liquid crystal display device. That is, the manufacturing process for the transflective liquid crystal display device includes a process for producing an array substrate, which includes a plurality of the thin film transistors and pixel electrodes thereon, a process for producing a color filter substrate, which includes the color filter and the common electrode, and a process for producing a liquid crystal cell, which includes such processes as an alignment of the two substrates, an injection of the liquid crystal and sealing and forming the polarizer. The alignment of the array substrate and the color filter substrate is performed as follows. A number of seal patterns are formed on one of the array substrate and the color filter substrate and a number of spacers are dispersed on one of the two substrates to maintain a distance between the two substrates. The two substrates then are aligned in such a way that each of the sub-color filters corresponds to each of the pixel electrode and finally the two substrates are assembled by a pressure hardening of the seal pattern. If a misalignment of the array substrate and the color filter substrate occurs during the alignment process, inferiorities such as a leakage of light may be generated. The width of the black matrix on the second substrate may be formed wide enough to prevent the leakage of light but this tends to lower the aperture ratio of the liquid crystal display device.
Accordingly, the present invention is directed to a transflective liquid crystal display device and a method of manufacturing the reflective liquid crystal display device that substantially obviates one or more of the problems encountered due to the limitations and disadvantages of the related art.
An advantage of the present invention is to provide a transflective liquid crystal display device in which a color filter is formed on the lower substrate to increase luminance, and the luminance and color purity are controlled uniformly by controlling the thickness of the cell gap and the thickness of the color filter.
Another advantage of the present invention is to provide a method of manufacturing a transflective liquid crystal display device that has a color filter on a lower substrate and a black matrix or a buffer layer on an upper substrate.
Additional features and advantages of the present invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the present invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and the claims herein as well as the appended drawings.
To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, a transflective liquid crystal display device comprises a first substrate, a gate line and a data line defining a pixel region by crossing each other on the first substrate, a thin film transistor connected to the gate line and the data line, a passivation layer covering the thin film transistor and having a first transmission hole, a reflector disposed on the passivation layer in the pixel region and having a second transmission hole, a color filter formed on the reflector, a pixel electrode formed of a transparent conductive material formed on the color filter and connected to the thin film transistor through a contact hole, a second substrate spaced apart from the first substrate, a common electrode formed of a transparent conductive material provided beneath the second substrate, and a liquid crystal layer disposed between the pixel electrode and the common electrode. The pixel electrode may be partially overlapped with the data line and the reflector may be extended to cover the thin film transistor. The second substrate may further include a black matrix that corresponds to the thin film transistor, and a buffer layer, which has a third transmission hole corresponding to the first and second transmission holes, on the common electrode. The first substrate may further include an unevenness that is formed of the same material as the passivation layer in a position corresponding to the first and second transmission holes. The passivation layer may have an unevenness under the reflector. The first substrate may further include an insulating layer that is formed of an organic insulating material on the passivation layer. The transflective liquid crystal display device may further include a gate insulating layer between the gate line and the data line and thus the first and second transmission holes may further extended to the gate insulating layer.
A manufacturing method of a transflective liquid crystal display device comprises the steps of forming a gate line and a data line defining a pixel region by crossing each other on the first substrate; forming a thin film transistor connected to the gate line and the data line; forming a passivation layer covering the thin film transistor and having a first transmission hole; forming a reflector on the passivation layer in the pixel region and having a second transmission hole; forming a color filter on the reflector, forming a pixel electrode on the color filter using transparent conductive material, the pixel electrode being connected to the thin film transistor through a contact hole; forming a common electrode on a second substrate using a transparent conductive material, facing the first substrate and the second substrate toward each other and forming a liquid crystal layer between the pixel electrode and the common electrode. The pixel electrode may be partially overlapped with the data line and the reflector may be extended to cover the thin film transistor. The manufacturing method of the transflective liquid crystal display device may further include a step of forming a black matrix, which corresponds to the thin film transistor, on the second substrate. The manufacturing method of the transflective liquid crystal display device may further include a step of forming a buffer layer, which has a third transmission hole corresponding to the first and second transmission holes, on the second substrate. The step of forming the passivation layer may further include a step of forming unevenness under the reflector. The manufacturing method of the transflective liquid crystal display device may further include a step of forming an insulating layer on the passivation layer using an organic insulating material. The step of forming the passivation layer may further include a step of forming unevenness in a position that corresponds to the first and second transmission holes using the same material as the passivation layer.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.